By studying metabolites in urine samples from 1559 US citizens, researchers identified differences between the two groups. As well as giving urine samples, the participants were asked questions about their diet and had their blood pressure measured four times over three weeks. The researchers then sought links between the metabolites, the foods the participants said they ate and their blood pressure.

They found that diet could explain between a third and a half of the blood pressure difference seen between men in the two groups, and a quarter in women. Most of this is down to different food choices.

Compared with whites, African Americans consumed less of a number of key nutrients that could potentially lower blood pressure, including vegetable protein, iron, potassium and calcium. African Americans also consumed more of some substances known to raise blood pressure, including cholesterol and glycine, an amino acid found at higher levels in meats.

Co-author Jeremy Nicholson of Imperial College London says a genetic mechanism may be amplifying the effects of bad diet. "Microscopic variations in the genome, none of which are significant in their own right, change the risk of populations when they have risky behaviours [such as eating unhealthy food]," he says.

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